Neuron Specific Regulation of HSV1 and HSV2 Outcomes of Infection Abstract Our overall goal is to identify how different types of neurons regulate viral infections to produce divergent outcomes of lytic, latent or reactivating infections. It is well-established that herpes simplex viruses (HSV1 and HSV2) establish latency in sensory and autonomic neurons, from which they can reactivate to cause recurrent disease. However, some types of neurons support HSV replication upon entry, while other types naturally inhibit viral replication, resulting in latency. Exogenous stimuli can trigger reactivation, but only from a portion of these latently infected neurons. The neuronal populations that support these divergent outcomes differ for HSV1 and HSV2, leading to different anatomical patterns and frequencies of recurrent disease. To fully understand how mature sensory neurons permit or inhibit viral replication, it is essential to study these mechanisms in the appropriate neurons. We have determined that in adult sensory neurons, continuous presence of glial cell derived neurotrophic factor (GDNF) and neurturin (NTN) maintain HSV latency through their receptors, GFR?1 and GFR?2. Deprivation of GDNF or NTN selectively induces HSV2 or HSV1 reactivation. GFR?1/2 signaling through RET activates several downstream signaling pathways to maintain cellular function, and also maintains the presence of proteins bound to specific regions of the viral genome. The central hypothesis of this proposal is that that GDNF and NTN continuously signal through RET to maintain HSV1 and HSV2 in a latent state in adult sensory neurons. Furthermore, continuous signaling deposits inhibitory neuronal proteins onto the viral genome, including chromatin modifications associated with inactive gene transcription. Using our innovative primary adult sensory neuronal cultures, combined with an in vivo model that recapitulates the different HSV1 and HSV2 recurrence patterns, we will 1) identify the neuronal signaling pathways through which neurotrophic factors regulate HSV1 and HSV2 infections, 2) determine how neurotrophic factors maintain the latent state of the viral genome, and 3) determine how neurotrophic factor deprivation differentially induces HSV1 and HSV2 reactivation in vivo. The rationale that drives this project is that by identifying neuronal factors and mechanisms that naturally prevent HSV replication and reactivation in specific types of neurons, we can identify targetable neuronal pathways and factors to permanently lock the virus into a latent state incapable of reactivation, in any type of neuron.